Photodetection in the ultraviolet (UV) region has gained significant focus in recent years due to its wide range of applications, such as security, chemical detection, and military and lethal substance detection. Compared with Si-based UV photodetectors, which are based on low bandgap materials and work inefficiently over the UV spectrum, photodetectors based on III-V nitrides, such as AlGaN and GaN, possess several advantages, including solar-blind spectral selectivity, high breakdown field, high thermal stability, radiation hardness, and high responsivity. Structures including p-i-n diodes and metal-semiconductor-metal have been explored to improve performances, including high signal-to-noise ratio, fast transient response, high responsivity, high spectrum selectivity, and low dark current. However, UV detectors that meet all the requirements with one design have not yet been developed, because the traditional architectures of the photodetectors are not designed to work optimally over the short wavelength spectrum. The shallow penetration depth and the strong surface recombination within the highly doped contact layer are limiting factors in the operation of UV detectors.
AlGaN/GaN HEMTs have been used as UV detectors. The high mobility of the 2DEG and the low doping profile of the whole structures yield a high-speed response for these UV detectors. Although electron transportation in the 2DEG layer is robust and fast, the carriers on the surface of AlGaN suffer from surface recombination and short lifetimes.